Thursday, December 31, 2009

Eight creatures that live on the edge

Eight creatures that live on the edge

Forget BASE jumping and snowboarding - you need a microscope to find the most impressive examples of a life truly lived at the extreme. 'Extremophiles' can be found thriving in conditions from concentrated acid to radioactive waste. Meet the microbes that never say die.


Fungi are known for chowing down on anything, but even in this company C. sphaerospermum stands out. That's because it thrives on radiation. Researchers from the Albert Einstein College of Medicine in New York City, believe that the black fungus converts ionising radiation into usable energy, just as green plants convert sunlight. It appears that C. sphaerospermum copes with the DNA-damaging effects of radiation by having multiple copies of the same chromosome in every cell. This fungus is happy living even in the heart of the Chernobyl reactor, where it was discovered in 1999.


Not many bacteria have a nickname, but D. radiodurans has earned its moniker, Conan the Bacterium. It is one of the most radiation-resistant organisms on Earth, able to withstand 10,000Gy (measurement unit for absorbed radiation) of ionising radiation. In contrast, just 5Gy can kill a human. D. radiodurans is also able to deal with UV radiation, desiccation and extreme cold. Like any true hero, its power is now being used for good: D. radiodurans and other bacteria from the same genus are now being engineered to help clean up radioactive sites left over from the Cold War.


Fifty to 60oC is hot enough to scald a person, but it's perfect for the thermophilic bacterium C. aurantiacus. It's found growing in a hot spring in Yellowstone National Park, USA, where it uses a primitive kind of photosynthesis to get its energy from light. But unlike most photosynthetic organisms, C. aurantiacus is not restricted to places where it can see the Sun: this versatile bacterium also grows happily in the dark using aerobic respiration.


If C. aurantiacus likes it hot, another likes it boiling. P. furiosus thrives in 100°C environments around sulphurous volcanoes on the sea floor. Some extremophiles have slow generation times to cope with their living conditions, but not this 'hyperthermophile': it can reproduce in just 37 minutes. Instead, P. furiosus deals with heat-induced DNA damage by having a DNA-building enzyme with proofreading capabilities, called pfu polymerase. The enzyme works so well that it has become one of the most important tools in DNA research.


Fancy living in battery acid? The microbial colonies that form snottites do it with ease. Simple colonies of fungi and bacteria, mostly from the genus Acidithiobacillus, snottites are found in limestone caves where sulphur-rich water comes into contact with oxygen. They oxidise hydrogen sulphides to get energy and produce sulphuric acid, so their immediate environment is very acidic, with a pH of between zero and one. Because the colonies are so simple - usually just a few species - and because they are isolated in their caves, snottites are important models for studying bacterial ecology and evolution. And the name? The colonies hang down from cave roofs in gooey formations that have the consistency of, well, snot.


S. Americana grows in a bleach-like pH of 8 to 10 in Mono Lake, a large volcanic basin in California. The lake has no outlets, so evaporation has left a super-salty, alkaline environment for S. Americana, which lives in the oxygen-less mud at the bottom. Astrobiologists hope that fossils of similar 'haloalkaliphiles' may be found in the Gusev Crater on Mars, which may once have been a landlocked lake like Mono.


A flatulent cow's stomach may not be your idea of a good home, but for a capnophile - a lover carbon dioxide - like M. succiniciproducens, it's heaven. M. succiniciproducens converts CO2 into succinic acid, a precursor to the fatty acids that its cow host can use as energy. Succinic acid is also an important industrial chemical, used to produce biodegradable


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